1. Field of the Invention
The present invention relates to a method and an apparatus for soldering and, more specifically, to a method and an apparatus for soldering electronic components to a substrate.
2. Description of the Related Art
Soldering is employed in many cases as a method for bonding electronic components to substrates. By employing soldering, it is possible to fix an electronic component to a substrate and to electrically connect a terminal formed in the electronic component with a terminal formed on the substrate at the same time. For example, as will be described later, it can be employed for soldering a magnetic head slider (an electronic component) to a suspension (flexure) to which a flexible printed board is unified, when manufacturing a head gimbals assembly that is loaded on a magnetic disk device.
However, when the bonding target by executing soldering is an electronic component as in the case described above, the electronic component may be increased to a high temperature of more than its heat resistant property due to the heat applied at the time of soldering. This may cause such a problem that the heat of the soldering damages the electronic component. Therefore, conventionally, heating of solder by a laser or the like is limited to a short time. Further, as in Patent Document 1 mentioned below, there is also a method disclosed in which heat released from the main body of the electronic component as a bonding target is measured at the time of soldering, and the heating action is controlled so that the electronic component is soldered at a temperature lower than its heat resistant property. In the meantime, when the heating time for soldering is limited to a short time, fusion of solder becomes insufficient because the heating time is not long enough. Thus, stable soldering cannot be achieved.
Further, when soldering two bonding targets, e.g. when soldering an electronic component to a substrate, a temperature increase rate of each bonding pad of each bonding target may become different depending on the structures of the respective bonding targets, soldering conditions, and the like. In that case, if the temperature increase rates of those bonding pads are different by a great extent, one of the bonding targets remains to be in a low temperature. Therefore, soldering cannot be performed securely. In the meantime, when too much heat is applied to the solder for achieving secure soldering, the temperature of the other bonding target may be excessively increased. This may cause damages to the other bonding target by the heat. An example of such case will be described by referring to a case of soldering a magnetic head slider to a suspension (flexible printed board) of a head gimbals assembly that is loaded on a disk device, by referring to FIG. 1A to FIG. 6B.
For soldering a magnetic head slider, first, as shown in FIG. 1A, a magnetic head slider 102 having a magnetic head element 121 is sucked and held to a transporting nozzle 104, and the transporting nozzle is moved in a direction shown by an arrow Y101 so as to place the magnetic head slider 102 at a bonding point on a flexible printed board 113 that is unified on a flexure 112. At this time, as shown in FIG. 1B, for example, the magnetic head slider 102 is placed in such a manner that a slider-side pad 122 formed in the magnetic head element 121 of the magnetic head slider 102 comes close to a suspension-side pad 114 formed on the flexible printed board 113.
Thereafter, as shown with an arrow Y102 of FIG. 1A, a laser irradiating nozzle 106 having a solder ball 103 sucked and held at its tip is moved so that the solder ball 103 is abutted against the slider-side pad 122 and the suspension-side pad 114, which are to be solder-bonded. Under this state, laser beam L101 is irradiated to the solder ball 103 from the laser irradiating nozzle 106.
Upon this, the solder ball 103 to which the laser beam L101 is irradiated is fused and supposed to bond each pad. However, it is sometimes difficult to apply heat uniformly to the each of the bonding pads 122 and 114, i.e. the magnetic head slider side and the suspension side. Particularly, in this example of soldering, the magnetic head slider 102 is sucked or in contact with the transporting nozzle 104. Thus, as shown with the arrows of FIG. 2A, the heat applied by the laser beam L101 from the laser irradiating nozzle 106 and transmitted to the slider-side pad 122 is absorbed by the magnetic head slider 102 and the transporting nozzle 104. Therefore, the temperature of the slider-side pad 122 becomes lower than the temperature of the suspension-side pad 114 at the time of soldering, so that it becomes difficult to have the solder bonded to the slider-side pad 122. As shown in FIG. 2B, this results in having poor soldering, such as having the solder 103 remained only on the suspension-side pad 114.
In the meantime, when the laser beam L101 with a high energy is irradiated from the laser irradiating nozzle 106 (see FIG. 3A) in order to avoid the poor soldering described above, an excessive amount of heat may be applied to the suspension-side pad 114, even though it allows the low-temperature slider-side pad 122 to be heated to a proper temperature for achieving the soldering. If so, as shown in FIG. 3B, there is a possibility of having a damage D by the heat generated in a structure near the suspension-side pad 114, such as on a polyimide layer that forms the flexible printed board.
FIG. 4A to FIG. 5B are photographs of a head gimbals assembly to which soldering is actually performed. FIG. 4A and FIG. 4B show a state (pre-bumping) where: the magnetic head slider 102 is placed on the suspension 112; the solder ball 103 is set between each of the bonding pads 122 and 114 to be bonded; and the solder ball 103 is heated at that bonding point to be tentatively fixed so that a part of the solder ball 103 is being fused. Further, FIG. 5A and FIG. 5B show a state (reflow) where the solder 103 is completely fused for securely bonding each of the bonding pads 122 and 114. FIG. 4A and FIG. 5A are photographs of the head gimbals assembly viewed from the magnetic head slider 102 side, and FIG. 4B and FIG. 5B are photographs viewed from the back face side (the polyimide layer 113 side of the flexible printed board). The numbers applied in the photographs indicate the positions of the respective bonding pads 122 and 114. That is, in this case, there are six soldering points. Further, FIG. 6A shows energies of the laser applied to each solder ball 103 (each bonding pad) at the time of pre-bumping shown in FIG. 4A and FIG. 4B, and FIG. 6B shows the energies of the laser applied to each solder ball 103 (each bonding pad) at the time of reflow shown in FIG. 5A and FIG. 5B.
With the soldering method described above, when the solder 103 is fused ad bonded between each of the bonding pads 122 and 114 so as to achieve highly reliable soldering, the damage D by the heat is generated in the structure near the suspension-side pad 114, i.e. on the polyimide layer that forms the flexible printed board, as indicated with a reference code D in FIG. 5B.    Patent Document 1: Japanese Unexamined Patent Publication 2004-260019